Activation of a material containing alkaline-earth metal carbonate and alkaline-earth metal hydroxide for the dry scrubbing of flue gas

ABSTRACT

The invention relates to a method for increasing the absorbency of a material containing alkaline-earth carbonate and alkaline-earth hydroxide with regard to sulfur oxides and/or other pollutants, in particular in flue gas, wherein the material containing alkaline-earth carbonate and alkaline-earth hydroxide is activated by heating said material to approximately 250° C. to approximately 750° C. for a time period of 1 minute to 12 hours.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/290,201, filed Oct. 11, 2016, now U.S. Pat. No. 10,532,313,issued Jan. 14, 2020, which is a continuation application of U.S. patentapplication Ser. No. 14/388,429, filed Feb. 17, 2015, which claimspriority under 35 U.S.C. § 371 to Patent Cooperation Treaty ApplicationNo. PCT/EP2013/056904, filed Apr. 2, 2013, which claims the benefit ofearlier filed European Patent Application No. 12162517.2, filed Mar. 30,2012. The entire contents of the aforementioned applications are herebyincorporated by reference herein in their entirety, including drawings.

The invention relates to a method for increasing the absorbency of amaterial containing alkaline-earth metal carbonate and/or alkaline-earthmetal hydroxide in relation to sulphur oxides and/or other pollutants,particularly in flue gas. The invention furthermore relates to anactivated material containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide produced by this method, and to the useof this material for off-gas scrubbing, in particular for dry flue gasscrubbing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the rate of reduction in the values of the degree ofdeposition when deposition drops by either 90%, 70% or 50% attemperatures that range from 200° C. to 900° C. Untreated referencematerial is compared to sample materials at different temperatures.

FIG. 2 shows how the SO₂ absorbency varies when the materials areactivated for different lengths of time and at different temperatures.

In the field of off-gas scrubbing, numerous methods are employed.Besides wet off-gas scrubbing, dry off-gas scrubbing is also employed.Materials containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide, in particular lime products, are used invarious dry flue gas scrubbing processes as sorbents for the depositionof acid-forming off-gas components in various temperature ranges.

The aim is to neutralise the acidic pollutants present in the off-gasflow, such as sulphur dioxide, hydrogen chloride and hydrogen fluoride,and to deposit on suitable deposition devices the neutral salts formed.In this case, for example, bed filters, entrained-flow processes, inconjunction with electro-filters or fabric filters, are used.

Dry off-gas scrubbing is used in different variants. The most essentialfields of use are scrubbing the off-gases of coal and lignite powerstations, waste incineration plants, hazardous waste incinerationplants, heat engines and furnaces with various fuels.

One widespread technique in the temperature range of up to mostly about200° C. is the bed filter technique. In this case, sorbents based onlimestone (CaCO₃), in particular granulated or pelleted products basedon limestone (CaCO₃) and/or lime hydrate (Ca(OH)₂), and/or thecorresponding dolomitic products are used. In these filters, the off-gasto be scrubbed flows through a granular bed of material containingalkaline-earth metal carbonate and/or alkaline-earth metal hydroxide.Here, deposition of the acidic off-gas components on the material(sorbent) containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide takes place.

With the aid of off-gas scrubbing, the off-gases containing pollutantscan be very substantially scrubbed. A disadvantage, however, is that theconsumption of sorbent containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide is very high. The moderate efficiency ofdry off-gas scrubbing is attributable to the fact that the sorbents donot react fully through. A layer of reaction products, which makesfurther penetration of the acidic pollutants to be deposited difficult,is formed on the sorbent.

A deficiency of the bed filter technique is the relatively highconsumption for the deposition of sulphur oxides (SO₂ and SO₃) and thesealing of the reactive surface of the sorbents by the reaction productsbeing formed, for example calcium sulphite (CaSO₃) and calcium sulphate(CaSO₄).

Attempts have repeatedly been made to reduce the high sorbentconsumption. One method consists in mechanically reprocessing thedeposited product, which consists of unreacted sorbent and the reactionproducts formed, after the off-gas scrubbing. The intent and purpose ofthe mechanical treatment is to separate the unreactive outer layers.Another method provides intermediate storage of the reaction productwith reuse after 1-2 days of storage.

All these methods, however, are characterised by insufficienteffectiveness in terms of increasing the absorbency of the sorbent.

Increasing the absorbency of the sorbent is intended to mean reducingthe amount of sorbent to achieve a particular degree of deposition ofthe acidic pollutants. A higher absorbency in this case leads to areduction in the stoichiometric factor.

There is significant interest in producing activated materialscontaining alkaline-earth metal carbonate and/or alkaline-earth metalhydroxide, which have an increased absorbency in relation to sulphuroxides and/or other pollutants in the flue gas.

This object is achieved according to the invention by a method forincreasing the absorbency of a material containing alkaline-earth metalcarbonate and/or alkaline-earth metal hydroxide in relation to sulphuroxides and/or other pollutants, particularly in flue gas, in which thematerial containing alkaline-earth metal carbonate and/or alkaline-earthmetal hydroxide is activated by heating to from about 200° C. to about850° C.

In the context of this invention, a material containing alkaline-earthmetal carbonate and/or alkaline-earth metal hydroxide is intended tomean all materials which contain at least one alkaline-earth metalcarbonate and/or alkaline-earth metal hydroxide, or consist of one ofthese substances. In particular, according to the invention a materialcontaining alkaline-earth metal carbonate and/or alkaline-earth metalhydroxide is intended to mean both lime and dolomite derived material.According to a preferred embodiment of the invention, the materialcontaining alkaline-earth metal carbonate and/or alkaline-earth metalhydroxide contains calcium carbonate, calcium hydroxide, magnesiumcarbonate and/or magnesium hydroxide, or consists of one of thesesubstances.

According to the invention, alkaline-earth metal carbonates are intendedto mean all salts and esters of carbonic acid, i.e. in particularsecondary carbonates, hydrogen carbonates, orthocarbonates and carbonateesters, which contain an alkaline-earth metal. The alkaline-earth metalsinclude inter alia magnesium, calcium, beryllium, strontium and barium.According to a preferred embodiment of the invention, the alkaline-earthmetal carbonate is magnesium carbonate or calcium carbonate, or amixture thereof. Alkaline-earth metal carbonates particularly suitableaccording to the invention are present in products derived from limeand/or dolomite. According to a preferred embodiment of the invention, amaterial based on limestone and/or dolomite is used as the materialcontaining alkaline-earth metal carbonate. For example, unburnt and/orpartially burnt lime has been found to be suitable according to theinvention. Furthermore, unburnt and/or partially burnt dolomite has beenfound to be suitable according to the invention. Burnt lime and/or burntdolomite are likewise suitable.

According to the invention, alkaline-earth metal hydroxides are intendedto mean all compounds which contain an alkaline-earth metal and themonovalent group of atoms —OH as a functional group or ion. Thealkaline-earth metals include inter alia magnesium, calcium, beryllium,strontium and barium. According to a preferred embodiment of theinvention, the alkaline-earth metal hydroxide is magnesium hydroxide orcalcium hydroxide, or a mixture thereof. Alkaline-earth metal hydroxidesparticularly suitable according to the invention are present in productsderived from lime and/or dolomite. According to a preferred embodimentof the invention, a material based on lime hydrate (slaked lime) and/ordolomite hydrate is used as the material containing alkaline-earth metalhydroxide. For example, slaked and/or partially slaked lime has beenfound to be suitable according to the invention. Furthermore, slakedand/or partially slaked dolomite has been found to be suitable accordingto the invention.

According to a preferred embodiment of the invention, the materialcontains both alkaline-earth metal carbonate and alkaline earth metalhydroxide.

Surprisingly, it has been found that the deposition capacity ofmaterials containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide in relation to acidic gas components, inparticular sulphur dioxide in flue gas, can be improved when thematerial is heated to temperatures of between about 200° C. and about850° C. Without wishing to be bound by scientific theory, it appearsthat the heating leads to activation of the sorbents containingalkaline-earth metal carbonate and/or alkaline-earth metal hydroxide.Thus, a significant increase in the absorbency of materials (sorbents)containing alkaline-earth metal carbonate and/or alkaline-earth metalhydroxide is already achieved by single heating to temperatures ofbetween about 200° C. and about 850° C.

By the method according to the invention, the absorbency of a materialcontaining alkaline-earth metal carbonate and/or alkaline-earth metalhydroxide can be increased particularly in relation to sulphur oxides,such as sulphur dioxide (SO₂) and/or sulphur trioxide (SO₃), and/orother pollutants, in particular hydrogen chloride (HCl) and/or hydrogenfluoride (HF).

The method according to the invention thus allows more effectivedeposition of pollutants and, hence, minimization of the demand formaterial (sorbent) containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide in dry flue gas scrubbing.

According to a particularly preferred embodiment of the invention, thematerial contains both alkaline-earth metal carbonate and alkaline-earthmetal hydroxide. The proportion of alkaline-earth metal carbonate andalkaline-earth metal hydroxide in the material may vary in wide ranges.The proportion of alkaline-earth metal carbonate in the materialpreferably varies in the range of from 10 wt. % to 90 wt. %, morepreferably from 20 wt. % to 60 wt. %, and in particular from 25 wt. % to30 wt. %, in each case based on the total amount of material.

For a material containing both alkaline-earth metal carbonate 20 andalkaline-earth metal hydroxide, the proportion of alkaline-earth metalhydroxide in the material preferably varies in the range of from 10 wt.% to 90 wt. %, more preferably from 40 wt. % to 80 wt. %, and inparticular from 70 wt. % to 75 wt. %, in each case based on the totalamount of material.

According to a preferred embodiment of the invention, the activation ofthe material containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide, in particular of the material containingalkaline-earth metal carbonate and alkaline-earth metal hydroxide, ispreferably carried out in air.

Practical tests have shown that a particularly strong increase in theabsorbency of the sorbent, can be achieved when the material containingalkaline-earth metal carbonate and/or alkaline-earth metal hydroxide isheated to temperatures of from about 250° C. to about 750° C.,preferably from about 250° C. to about 700° C., in particular from about300° C. to about 500° C. According to the invention, the materialcontaining alkaline-earth metal carbonate and/or alkaline-earth metalhydroxide is preferably heated to temperatures of from about 250° C. toabout 750° C. It has been observed that the activation effect accordingto the invention no longer occurs above about 850° C. This is probablybecause less readily absorbing burnt products are formed at thesetemperatures. When using lime-derived material, for example, it has beenobserved that the less readily absorbing calcium oxide is formed atactivation temperatures above about 850° C. When heating to temperaturesbelow 200° C., likewise no significant activation of the alkaline-earthmetal carbonate and/or alkaline-earth metal hydroxide was observed.

According to a particularly preferred embodiment of the invention, thelevel of the activation temperature is selected as a function of theproportion of alkaline-earth metal carbonate and/or alkaline-earth metalhydroxide in the material.

If the proportion of alkaline-earth metal carbonate in the material ismore than 50 wt. %, preferably from 55 wt. % to 90 wt. %, and inparticular from 60 wt. % to 70 wt. %, then it has been found expedientto set the activation temperature at 5 values of at least 350° C.,preferably from 350° C. to 700° C., more preferably from 400° C. to 600°C.

If the proportion of alkaline-earth metal hydroxide in the material ismore than 50 wt. %, preferably from 50 wt. % to 90 wt. %, and inparticular from 70 wt. % to 75 wt. %, then it has been found expedientto set the activation temperature at values of at most 600° C.,preferably from 250° C. to 550° C., more preferably from 350° C. to 450°C.

The heating of the material containing alkaline-earth metal carbonateand/or alkaline-earth metal hydroxide may be carried out in various waysknown to the person skilled in the art. For example, the heating may becarried out in a kiln or by passing over hot off-gas in a fluidised bedor fluid bed, or in bed filters.

The duration for which the material containing alkaline-earth metalcarbonate and/or alkaline-earth metal hydroxide is heated, and thereforeactivated, may vary in wide ranges. In particular, it has been foundthat the optimal activation time depends on the material used and theactivation temperature selected. The person skilled in the art candetermine the optimal activation parameters, in particular activationtime and activation temperature, for a particular material by test runs.

For reasons of energy, it is advantageous to limit the duration of theheating. It has been found particularly expedient to heat the materialcontaining alkaline-earth metal carbonate and/or alkaline-earth metalhydroxide for a duration of from 1 minute to 12 hours, preferably from10 minutes to 12 hours, particularly preferably from 1 hour to 6 hours,in particular from 2 to 5 hours. According to the invention, thematerial containing alkaline-earth metal carbonate and/or alkaline-earthmetal hydroxide is preferably heated for a duration of from 1 minute to12 hours. In the case of very fine-grained materials and/or suitableselection of the activation temperature and an optimised heating method,shorter heating times are also possible.

According to one embodiment of the invention, the material containingalkaline-earth metal carbonate and/or alkaline-earth metal hydroxide isactivated in a separate step by the method according to the inventionbefore it is used as a sorbent.

Tests have shown that the thermal activation according to the inventionalso persists when the material containing alkaline-earth metalcarbonate and/or alkaline-earth metal hydroxide is cooled again afterthe activation. According to one embodiment of the invention,accordingly, the activated material containing alkaline-earth metalcarbonate and/or alkaline-earth metal hydroxide is cooled to roomtemperature in a further step.

According to another embodiment of the invention, the materialcontaining alkaline-earth metal carbonate and/or alkaline-earth metalhydroxide is heated in the scope of its use in dry flue gas scrubbingonce or continuously to temperatures of from about 200° C. to about 850°C., preferably from about 250° C. to about 750° C., in particular fromabout 300° C. to about 500° C. The material containing alkaline-earthmetal carbonate and/or alkaline-earth metal hydroxide may, according toanother embodiment, already be contained in a filter ready for use forthe flue gas scrubbing when it is heated, particularly a bed filter or afilter cartridge.

According to the invention, all materials based on limestone and/ordolomite, which are suitable for the deposition of acidic components influe gas, and in particular sulphur dioxide, are suitable in particularas materials containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide. Particularly good results are achievedwhen using products with a particularly large surface area, derived fromlime or dolomite, which are specially developed for flue gas scrubbing.According to a preferred embodiment, calcium hydroxide and/or calciumcarbonate, as well as products which partially contain calcium hydroxideand/or calcium carbonate, are used as the material containingalkaline-earth metal carbonate and/or alkaline-earth metal hydroxide.

Practical tests have shown that the thermal activation according to theinvention works particularly well for materials which at least partiallycontain alkaline-earth metal hydroxides. Particularly good activationsare reached when the material has an alkaline-earth metal hydroxidecontent of from 1 to 100 wt. %, for example an alkaline-earth metalhydroxide content of from about 5 to about 25 wt. %, or from about 10 toabout 15 wt. %. The alkaline-earth metal hydroxide content may inparticular be selected from the group consisting of more than about 5wt. %, more than about 15 wt. %, more than about 25 wt. % and more thanabout 50 wt. %. Practical tests have shown that very good thermalactivations are likewise achieved with alkaline-earth metal hydroxidecontents of from about 60 to about 90 wt. %.

The particle size of the material containing alkaline-earth metalcarbonate and/or alkaline-earth metal hydroxide may vary in wide ranges.Particularly good deposition capacities are achieved with granules aswell as granulated or pelleted products. The particle sizes of thegranules, or granulated or pelleted materials, preferably vary in therange of from about 0.1 to about 50 mm, particularly preferably betweenabout 1 mm and about 10 mm, and in particular between about 2 mm andabout 6 mm.

The activated product containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide, produced by the method according to theinvention, is outstandingly suitable as a sorbent for the absorption ofsulphur oxides, in particular sulphur dioxide (SO₂) and/or sulphurtrioxide (SO₃), and/or other pollutants, in dry flue gas scrubbing.Furthermore, the present invention also relates to a product containingalkaline-earth metal carbonate and/or alkaline-earth metal hydroxideproduced by the method according to the invention, as well as to its usein off-gas scrubbing, particularly in dry flue gas scrubbing.

Practical tests have shown that particularly good deposition capacitiesare achieved when the material containing alkaline-earth metal carbonateand/or alkaline-earth metal hydroxide is used as a filler material in abed filter. In this embodiment of the invention, the gas to be scrubbedflows through a loose granular layer of material containingalkaline-earth metal carbonate and/or alkaline-earth metal hydroxide,which is used as a filter medium. The particle size range of thematerial containing alkaline-earth metal carbonate and/or alkaline-earthmetal hydroxide is preferably between about 0.1 mm and about 10 mm, morepreferably between about 2 mm and about 6 mm, in particular betweenabout 3 mm and about 5 mm. In this case either the activation accordingto the invention may be carried out during operation of the bed filter,or the material containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide may be activated beforehand, i.e. beforeit is used as a sorbent in the bed filter.

The flow speeds in the bed filter may vary in wide ranges. For example,speeds of between 0.1 m/s and 5 m/s may be set. Depending on therequired degree of deposition and pressure loss, the layer heights maybe up to a few metres. Preferred layer heights lie in the range of fromabout 100 mm to about 500 mm, in particular from about 200 mm to about400 mm.

The deposition of particles in bed filters may, according to theinvention, take place in a fixed bed (stationary bed), a fluid bed, amigrating bed (moved bed) and a fluidised bed (layer carried by the gasflow). The use of bed filters with 5 a stationary bed is particularlyexpedient.

According to a preferred embodiment of the invention, the operatingtemperature in the bed filter is increased to temperatures of more than200° C., and an increase in the absorbency of the material containingalkaline-earth metal carbonate and/or alkaline-earth metal hydroxide isthus achieved. For many materials containing alkaline-earth metalcarbonate and/or alkaline-earth metal hydroxide, a maximum of theeffectiveness may be achieved at an activation temperature of about 400°C.

It may be expedient to configure the increase in the operatingtemperature in the bed filter in such a way that both activation of thematerial and, simultaneously, a high deposition rate for pollutants, inparticular for SO₂, are ensured. Against this background, it has beenfound particularly expedient to set the operating temperature in the bedfilter at values of from 130° C. to 150° C., preferably from 280° C. to370° C.

As an alternative, it is also conceivable to set the operatingtemperature in the bed filter with a view to optimising the activationof the material and, simultaneously, to minimise the activation time. Inthis way, the duration during which the deposition rate is possibly notoptimal is minimised. Taking into account the fact that, as mentionedabove, the optimal activation temperatures depend on the composition ofthe material, and that the optimal deposition temperatures for SO₂ liein the range of from 280° C. to 370° C., the person skilled in the artcan readily determine the optimal relationships of activationtemperature and activation time.

As shown in FIG. 1, in the case of an increase in the activationtemperature with subsequent use of the activated material as a filtermaterial in the bed filter, a substantial improvement in the depositioncapacity takes place. A maximum of the effectiveness is in this caseachieved at about 400° C.

According to another embodiment according to the invention, however, itis likewise possible to carry out the heating of the material containingalkaline-earth metal carbonate and/or alkaline-earth metal hydroxidedirectly in the bed filter.

Operating temperatures of from about 200° C. to about 500° C.,preferably from about 220° C. to about 400° C., in particular from about250° C. to about 380° C., have been found to be expedient for this use.

For energy reasons, however, according to the invention it is preferredto heat the material containing alkaline-earth metal carbonate and/oralkaline-earth metal hydroxide before its use, for example once, to atemperature of between about 200° C. and about 850° C.

The essential advantages of this procedure according to the inventionare as follows:

1. The method is energy-efficient, since the filter does not have to beoperated constantly at high temperatures. By suitable setting of theactivation temperature and activation time as a function of thecomposition of the sorbent, the energy balance can be optimised.

2. The filter can be operated as before at the conventional lowtemperatures below 200° C., and therefore more cost-efficiently.

3. The activation by heating may be carried out either at themanufacturer of the material (sorbent) containing alkaline-earth metalcarbonate and/or alkaline-earth metal hydroxide, or by single periodicheating in the filtering process.

4. The demand for material containing alkaline-earth metal carbonateand/or alkaline-earth metal hydroxide can be minimised by more effectivedeposition.

The method according to the invention will be explained in more detailbelow with the aid of exemplary embodiments.

EXAMPLE 1

In a laboratory test, the effect of thermal activation on the absorbencyof a sorbent for dry flue gas scrubbing was studied. A sorbent was usedconsisting of granules that contain about 90 wt. % calcium carbonate andabout 10% wt. % lime hydrate. First, the sorbent was divided into 7batches of 200 g. The first batch was used as a reference sample, andwas not treated further. Batches 2 to 7 were stored for 6 hours incorrespondingly thermally regulated kilns at 200° C., 300° C., 400° C.,500° C., 600° C. or 900° C. The differently activated sorbents weresubsequently cooled to room temperature and the cartridge, respectivelyprovided therefor, of a 160 ml laboratory bed filter was filledtherewith. For each material, the absorbency was then determined incomparison with the reference material by recording SO₂ permeationcurves in the laboratory bed filter. To this end, the bed filters filledwith the sample material activated at different temperatures, orreference material, were flowed through at 160 to 170° C. by a likewisethermally regulated N₂/SO₂ test gas mixture with an SO₂ concentration of2000 ppm. The gas in this case flowed through the filter with a speed of0.1 m/s at a pressure of about 30 to 60 mmWC (residence time about 2 s).Arranged downstream of the filter there was a computer-assistedcontinuous gas analysis unit (company MSI, Type MSI 2000), whichrecorded the SO₂ concentration in the flow through the filter. Thedifference between the SO₂ concentration before the filter (2000 ppm)and after the filter was calculated as the degree of deposition. At timezero, the degree of deposition in all cases was 100%, i.e. the filtermaterial was capable of fully retaining the SO₂ in the test gas flowingthrough. Beyond a certain time, however, a reduction in the degree ofdeposition was found, i.e. permeation of SO₂ in the flow through thefilter, which is probably due to gradual saturation of the sorbent withSO₂. The greater the absorbency of the sorbent is, the longer SO₂ in thetest gas is retained in the filter, and the slower the reduction in thevalues of the degree of deposition, or of the SO₂ permeation takesplace. Characteristic values are the times after the start of the testat which the degree of deposition has fallen below 90%, 70% or 50%.These values are plotted in FIG. 1 for the untreated reference materialand the sample materials activated at different temperatures.Surprisingly, it was found that single thermal activation of the sorbentalready led to a strong increase in the absorbency. Thus, a materialwhich has been activated at 400° C. shows an increase in the SO₂absorbency by about 200% compared with the reference material. Even withan activation temperature of only 200° C., slight improvements in theabsorbency of the material activated in this way were found. With anactivation temperature of 900° C., on the other hand, the absorbency wasdegraded. Best results were achieved with activation temperatures offrom 200 to 600° C., and in particular from 300 to 500° C.

EXAMPLE 2

In a second test run, the effect of the activation time on theabsorbency of the material was studied. To this end, a procedurecorresponding to the conduct of the experiments according to Example 1was adopted. Merely the activation time (residence time in the kiln) wasvaried. In accordance with Example 1, the SO₂ absorbency of thematerials activated for different lengths of time and at differenttemperatures was studied. The results and the activation conditions areshown in FIG. 2. In this case, it is found that, the closer theactivation temperature is to 400° C., the shorter are the activationtimes required in order to achieve a relatively good absorbency. Forinstance, 30-minute activation at 400° C. shows approximately the sameimprovement in the absorbency as 12-hour activation at 300° C. The testsfurthermore show that, with an optimal activation temperature, shortactivation times (see FIG. 2, 5-minute activation at 400° C.) alreadylead to significant improvements in the absorbency compared with thereference material. For many activation temperatures, a furtherimprovement in the absorbency is shown with an increasing activationtime (cf. FIG. 2, 300° C. and 400° C.). For an activation temperature of500° C., on the other hand, 1-hour activation leads to better resultsthan 6-hour activation. As in Example 1, the material activated at 900°C. showed inferior absorbency than the reference material.

EXAMPLE 3

A bed filter filled with a sorbent containing alkaline-earth metalcarbonate and alkaline-earth metal hydroxide in a thermal power stationwas activated once by gas at a temperature of 400° C. flowing throughfor 2 hours. The bed filter was subsequently operated at a regularoperating temperature below 200° C. The thermal activation leads to animprovement in the pollutant absorbency of the bed filter by up to 300%.

EXAMPLE 4

Gas at a temperature of 270° C. flows through granules of CaCO₃ andCa(OH)₂ in an industrial fluid-bed process, the granules thereby beingdried and hardened. By lengthening the residence time, the material washeated beyond the drying point to the hot gas temperature, and therebyactivated. In this way, it was possible to achieve a 50% improvement inthe pollutant absorbency.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled) 11.A method for the absorption of sulphur oxides and/or other pollutants ina dry flue gas scrubbing comprising contacting the dry flue gas with anactivated material containing alkaline-earth metal carbonate andalkaline-earth metal hydroxide; wherein the activated material isactivated by a method comprising heating a material containingalkaline-earth metal carbonate and alkaline-earth metal hydroxide tofrom about 300° C. to about 500° C. for a duration of from 1 hour to 6hours.
 12. The method according to claim 11, further comprising the stepof providing the activated material containing alkaline-earth metalcarbonate and alkaline-earth metal hydroxide as filler material in a bedfilter before contacting it with the dry flue gas.
 13. The methodaccording to claim 12, wherein the activated material containingalkaline-earth metal carbonate and alkaline-earth metal hydroxide isactivated by heating the material containing alkaline-earth metalcarbonate and alkaline-earth metal hydroxide in the bed filter beforecontacting it with the dry flue gas.
 14. The method according to claim11, further comprising the step of providing the activated materialcontaining alkaline-earth metal carbonate and alkaline-earth metalhydroxide in a fluidised or fluid bed before contacting it with the dryflue gas.
 15. The method according to claim 11, wherein the step ofcontacting of the dry flue gas with the activated material containingalkaline-earth metal carbonate and alkaline-earth metal hydroxide isconducted in an entrained-flow process.